This invention relates to a vacuum circuit breaker particularly of the type having two breaking points.
In usual vacuum circuit breakers, open-close contacts, i.e., stationary and movable electric contacts, are provided in a vacuum chamber to easily extinguish an arc. The circuit breakers of this type include a double-breaking-point type circuit breaker in which two vacuum bulbs are connected in series for each phase.
In a typical example of the circuit breaker described above, three insulator brackets of a rod shape are secured one above the other to a rear part of a main frame of the breaker so as to extend substantially horizontally. The rear ends of the upper and lower insulator brackets support stationary electrode units, which are connected to a power source and a load, respectively. Vacuum bulbs are vertically arranged between the stationary electrode units with an intermediate supporting unit interposed therebetween. The outer side (stationary electrode side) portions of the vacuum bulbs are connected to the stationary electrode units and the inner side (movable electrode side) portions of the vacuum bulbs are supported on upper and lower sides of the intermediate supporting unit.
The rear end of the intermediate insulator bracket fixedly supports the intermediate supporting unit. The intermediate supporting unit has therein an operating mechanism connected to an operating mechanism in the main frame through an insulating operating rod which is horizontally arranged so as to operate the vacuum bulb operating unit accommodated in the intermediate supporting member. The upper and lower stationary electrode units are mechanically connected to the intermediate supporting unit through insulating plates.
With the vacuum circuit breaker of the type described, the end surfaces of the rear portions of the respective insulator brackets do not lie in the same vertical plane. This means that it involves much time to assemble together the stationary electrode units, the vacuum bulbs and the intermediate supporting unit in a mechanically well balanced condition. Furthermore, when the operating rod is operated to open or close the contacts in the vacuum bulbs, the intermediate supporting unit is caused to deform by a bending moment applied thereto, and hence, in case the vacuum circuit breaker is frequently operated, the intermediate insulator bracket may be broken in the worst case.